Experiments to improve chemistry learning by modelling

The process of modelling is inherently widespread in teaching approaches and in general human interaction with the world. When facing a new situation in their everyday life, students most common way of reacting is to ask for an example. This example can be then be seen as a model of the associated knowledge with some limitations. Models are indeed defined by their specific content and by the way they are elaborated or structured. In the context of science teaching, it is commonly observed that students misunderstand the exact role of models and underestimate their limitations. For instance, they often believe that models represent the unique truth, ignoring their inherent adaptability. Moreover, the importance of the modelling process and of an adequate analysis of the different dimensions spanned by the model concept itself is not sufficiently addressed in the various curricula. To overcome these misconceptions, a modelling approach is presented with the aim of helping students to become familiar with various scientific concepts associated with chemistry such as chemical kinetics, electrochemistry and chemical equations. In this study, modelling procedures have been developed within the framework of experimental activities. The active participation of students is promoted through the following activities: realizing and observing experiments dedicated to various concepts, modelling the associated results individually or in groups, taking part in guided discussions supervised by the teacher

Identification and frequency of consumption of wild edible plants over a year in central Tunisia: a mixed-methods approach

Objective: To identify wild plants used as food and assess their frequency of consumption over a year in a region of Tunisia where agriculture is undergoing a major transformation from smallholder farming to an intensive high-input agricultural system. Design: Qualitative ethnobotanical study followed by a survey of women's frequency of consumption of wild plants conducted using FFQ at quarterly intervals. Setting: Sidi Bouzid governorate of central Tunisia. Participants: Mixed-gender group of key informants (n 14) and focus group participants (n 43). Survey sample of women aged 20-49 years, representative at governorate level (n 584). Results: Ethnobotanical study: thirty folk species of wild edible plants corresponding to thirty-five taxa were identified by key informants, while twenty folk species (twenty-five taxa) were described by focus groups as commonly eaten. Population-based survey: 98 % of women had consumed a wild plant over the year, with a median frequency of 2 d/month. Wild and semi-domesticated fennel (Foeniculum vulgare Mill. and Anethum graveolens) was the most frequently consumed folk species. Women in the upper tertile of wild plant consumption frequency were more likely to be in their 30s, to live in an urban area, to have non-monetary access to foods from their extended family and to belong to wealthier households. Conclusions: In this population, wild edible plants, predominantly leafy vegetables, are appreciated but consumed infrequently. Their favourable perception, however, offers an opportunity for promoting their consumption which could play a role in providing healthy diets and mitigating the obesity epidemic that is affecting the Tunisian population

Modelling to understand chemical phenomena

Il existe actuellement un consensus sur le fait que les scientifiques ne décrivent pas la réalité telle qu’elle est dans toute sa complexité mais qu’ils en construisent des représentations qui leur permettent de l’expliquer partiellement et de la maîtriser, partiellement également. De telles représentations sont généralement appelées des modèles et le processus de leur construction est la modélisation. Les référentiels et programmes de sciences insistent de plus en plus, dans un souci d’authenticité épistémologique, sur la nécessité de confronter les élèves aux modèles établis et à leur élaboration, afin qu’ils se constituent une vision aussi fidèle que possible de l’entreprise scientifique. Le concept de modèle possède des composantes multiples et il n’est pas aisé d’en donner une définition compacte, complète et définitive. On pourrait tenter de dire, en bref, que modéliser, c’est simplifier délibérément pour pouvoir expliquer et agir efficacement. On peut envisager différents types de modèles qui ne s’excluent pas mutuellement. On les rencontrera dans les différentes activités expérimentales que nous proposons. (i) On peut tout d’abord modéliser une situation expérimentale complexe (une pile commerciale ou un accumulateur, par exemple) par une autre situation apparentée mais plus simple et dont on contrôle mieux les paramètres, afin de mettre leur influence en lumière. Diverses expériences sur les piles (de Daniell, entre autres) illustrent cet aspect. Les expériences proposées sur la diffusion entrent également dans cette catégorie. (ii) En chimie, le principe explicatif fondamental consiste à fonder les observations macroscopiques sur des processus décrits au niveau sub-microscopique (atomes, molécules, ions, électrons). Cette représentation sub-microscopique peut être schématique et/ou symbolique. Pour plusieurs des expériences proposées, on demande de représenter schématiquement les mouvements des particules concernées. On demande aussi de traduire le phénomène en un langage symbolique, l’écriture de la réaction chimique. Ici aussi, il s’agit d’une modélisation : quand on écrit HCl(aq), par exemple, on remplace une situation complexe et relativement mal définie – des ions H3O+ et des ions Cl- hydratés avec éventuellement plusieurs couches d’hydratation – par une écriture compacte qui représente de manière conventionnelle l’essentiel de l’information dont on a besoin dans un but déterminé (un titrage, par exemple)

Des pratiques enseignantes qui font obstacle au rôle des modèles dans la construction des savoirs scientifiques

Dans une perspective comparatiste, des didacticiens de plusieurs disciplines (biologie, chimie, histoire de l’art, mathématique et physique) ont étudié des pratiques enseignantes faisant obstacle au rôle des modèles dans la construction des savoirs scientifiques. Leur réflexion croisée les a amenés à considérer des niveaux élevés de l’échelle de codétermination didactique de Chevallard (2012) pour identifier des indicateurs d’une certaine forme de positivisme empirique dans l’épistémologie spontanée des enseignants. Cette posture s’exprime plus ou moins différemment d’une discipline à l’autre mais le fait que les modèles et théories enseignées ont fait ou non l’objet d’une standardisation au sein de communautés scientifiques savantes déterminent fortement leur transposition didactique. De ce point de vue, l’exemple de l’histoire de l’art a joué un rôle méthodologique important permettant de contraster et de questionner les pratiques dans les autres disciplines. Ce questionnement s’inscrit dans un objectif à plus long terme qui est la reproblématisation (au sens de Orange, 2005) d’enseignements relatifs aux disciplines enseignées

Antifungal activity and chemical composition of seven essential oils to control the main seedborne fungi of cucurbits

none9siEssential oils represent novel alternatives to application of synthetic fungicides to control against seedborne pathogens. This study investigated seven essential oils for in vitro growth inhibition of the main seedborne pathogens of cucurbits. Cymbopogon citratus essential oil completely inhibited mycelial growth of Stagonosporopsis cucurbitacearum and Alternaria alternata at 0.6 and 0.9 mg/mL, respectively. At 1 mg/mL, Lavandula dentata, Lavandula hybrida, Melaleuca alternifolia, Laurus nobilis, and two Origanum majorana essential oils inhibited mycelia growth of A. alternata by 54%, 71%, 68%, 36%, 90%, and 74%, respectively. S. cucurbitacearum mycelia growth was more sensitive to Lavandula essential oils, with inhibition of ~74% at 1 mg/mL. To determine the main compounds in these essential oils that might be responsible for this antifungal activity, they were analyzed by gas chromatography–mass spectrometry (GC-MS). C. citratus essential oil showed cirtal as its main constituent, while L. dentata and L. nobilis essential oils showed eucalyptol. The M. alternifolia and two O. majorana essential oils had terpinen-4-ol as the major constituent, while for L. hybrida essential oil, this was linalool. Thus, in vitro, these essential oils can inhibit the main seedborne fungi of cucurbits, with future in vivo studies now needed to confirm these activities.openMoumni M.; Romanazzi G.; Najar B.; Pistelli L.; Amara H.B.; Mezrioui K.; Karous O.; Chaieb I.; Allagui M.B.Moumni, M.; Romanazzi, G.; Najar, B.; Pistelli, L.; Amara, H. B.; Mezrioui, K.; Karous, O.; Chaieb, I.; Allagui, M. B

Imaging of hydrothermal altered zones in Wadi Al-Bana, in southern Yemen, using remote sensing techniques and very low frequency–electromagnetic data

© 2019, Saudi Society for Geosciences. Economic mineralization and hydrothermally altered zones are areas of great economic interests. This study focusses on hydrothermal altered zones of high mineralization potentials in Wadi Al-Bana, in southern Yemen. An azimuthal very low frequency–electromagnetic (AVLF-EM) data acquisition was conducted in search for mineralization in the study area. The study integrated observations from geophysical field data with others extracted from object-oriented principal component analysis (PCA) to better map and understand mineralization in the investigated area. This technique was applied to two data sets, ASTER and Landsat 8 Operational Land Imager (OLI) imagery. The results of PCA revealed high accuracy in detecting alteration minerals and for mapping zones of high concentration of these minerals. The PCA-based distribution of selected alteration zones correlated spatially with high conductivity anomalies in the subsurface that were detected by VLF measurements. Finally, a GIS model was built and successfully utilized to categorize the resulted altered zones, into three levels. [Figure not available: see fulltext.]

LEARNING CHEMICAL KINETICS AT SECONDARY SCHOOL LEVEL: MISCONCEPTIONS AND ALTERNATIVE APPROACH

Chemical kinetics occupies a central position in describing and understanding the dynamic behaviour of matter. It is then expected that this topic shares a significant part in the teaching curricula. Nevertheless, the review of the scarce literature on the topic reveals that little is usually invested to adequately include this field in the major programs. Most studies demonstrate that the teaching approaches in chemical kinetics often remain limited to the qualitative macroscopic description and do not identify the necessary relevant links between the macroscopic and the submicroscopic scales. Consequently, low levels of conceptual understanding and many misconceptions can be identified at the students’ level. Based on the constructivist approach in which the learners build their own cognitive structure, a new teaching sequence including qualitative and quantitative aspects of chemical kinetics for secondary school students (15-17 years old) is proposed. This teaching sequence allows the students to develop an ability to use corpuscular models as explanatory tools as well as an adequate conceptual understanding of chemical kinetics. This approach integrates visualization tools along with active learning strategies using, e.g., interactive websites